In a semiconductor circuit such as a semiconductor memory circuit, a potential higher than that supplied from a power supply is sometimes required for a purpose of realizing high speed operation or obtaining a predetermined level of reading or writing signals, so that various kind of booster circuits for boosting a potential have been used in such a semiconductor circuit. Such a conventional booster circuit comprises combinations of n-MOS transistors which are used as switching elements and bootstrap capacitors.
A first conventional booster circuit comprises a clock generator which generates a clock signal to be boosted, several n-MOS transistors and bootstrap capacitors. In the booster circuit, the clock signal supplied by the clock generator is "0" in an initial state, then is charged up to "V.sub.CC " which is a potential of a power supply, and finally is pushed up to "V.sub.DD " which is a potential higher than "V.sub.CC " by charged bootstrap capacitors through an n-MOS transistor.
A second conventional booster circuit comprises a clock generator which generates a control clock signal which has a potential level equal to or higher than that of a power supply, several n-MOS transistors, bootstrap capacitors and a delay circuit. In the booster circuit, a current flows through the n-MOS transistors to accumulate charges into a bootstrap capacitor, and an output signal is charged up to "V.sub.CC ", then finally the output signal is pushed up to "V.sub.DD " by the bootstrap capacitor storing the charges.
According to the conventional booster circuits, however, there are several disadvantages as described after. First, operation speed is not fast, because n-MOS transistors which are not fast in switching speed are used as switching elements. Second, a very high voltage is applied to a gate of an n-MOS transistor. This not preferably for the booster circuits in light of its reliability. Third, the booster circuits comprise many elements such as transistors, so that fabricating cost may be large. And finally, many bootstrap capacitors are required to be controlled, so that an error of operation may occur by skew of signals in the booster circuits.